How did the Moon form? Giant impact theory questioned

It seems that there’s always another Moon theory, or variation of an existing one, in the pipeline and here’s one of the newest contenders. Each seems to have its own issues though.

The most widely accepted theory about how the Moon formed has been challenged, with scientists saying a series of large impacts – rather than one giant collision – created our natural satellite, reports the IB Times.

By running numerical simulations, researchers say the Earth being hit by several large planetary bodies would help explain why our planet and the Moon are largely composed of the same material – a problem that has plagued scientists for decades.

The giant impact Moon formation theory was first proposed in the mid-1970s. It says a Mars-sized protoplanet called Theia smashed into Earth around 4.5 billion years ago. The ejected material created a disk of debris, molten rock and gas that eventually condensed to form the Moon.

However, there is a big problem with this theory. If it was correct, the Moon’s composition should be a mix of both Earth and Theia. For this to happen, Theia would have had to be almost identical to Earth in terms of its composition, which is highly unlikely.

A team of scientists from Israel has now come up with a potential solution. In a study published in Nature, they carried out almost 1,000 simulations of large – but not giant – planetary bodies impacting Earth. Their findings showed a series of big impacts could explain the Moon.
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However, the theory also comes with its own problems, he added. “Rufu et al. envision a scenario where following each impact, a new moonlet forms from the disk, migrates outwards and merges with the growing Moon,” he said. “Although they do not model the Moon’s accretion, their analysis suggests about 20 impacts are required to build the Moon — assuming perfect merging of every moonlet. If, as seems likely, merging is imperfect or some moonlets are lost, many more impacts may be required, thus making the necessary sequence of events far less probable than any of the more exotic single-impact scenarios.”

Concluding, he added: “For final adjudication, we must now look for firmer evidence on each side.”